A shopping cart is conventionally supported by a pair of fixed rear wheels and a pair of front swivel mounted wheels. These front directional swivel wheels are usually simply mounted to the cart underframe, without any suspension, since these carts should have the lowest manufacturing cost possible in view of the fact that they are leased free of charge to the customer during his/her stay into the grocery store. One problem encountered with these carts is the so-called "wobbling" of one of the swivel wheels or casters, when this wheel of the cart engages uneven terrain, or alternately, when the shopping cart underframe is slightly bent. A wobbling effect occurs because one of the swivel wheels becomes raised off the ground and may start to rotate or oscillate about its vertical axis. Once the raised swivel wheel resumes its ground engaging condition, it may have become transverse to the direction of travel of the shopping cart, thus creating a braking effect. The grocery items in the food basket supported by the shopping cart frame can thus be accidentally brought to roll or fall into the basket, thus undesirably damaging those groceries that are fragile (fruits, eggs, . . . ).
An initial attempt to address this swivel wheel wobbling problem at a low cost appears in U.S. Pat. No. 2,903,273 issued in September 1959 to the Tyler Refrigeration corp. In the Tyler patent, the front swivel wheels of the shopping cart are connected to a shopping cart cross-frame by a leaf-spring member 37 that allows the swivel mounted wheels 34, 30 to move upwardly and downwardly relative to the cart frame 13 under load. More particularly, and as illustrated in FIG. 3 of the Tyler patent, the elongated bell-shaped leaf spring 37 is anchored at its intermediate upper section to the cross-member 40 by pins 38, while its two opposite lower ends carry the two corresponding wheels 34. Although wheel wobbling with such a suspension is less likely, a new--and greater--problem is created, namely: an increased danger of lateral overturning. Indeed, the leaf spring 37 would tend to exacerbate any initial lateral tilt accidentally brought upon when the shopping cart is brought to a tight curve by the shopper, and thus possibly bring the whole basket 11 to fall laterally and strike ground along its side wall. Other carts, similar to shopping carts, often have a swivel wheel wobbling problem.